Fluid-operated oscillatory rotary actuators of the type embodying a radial vane mounted on a shaft for oscillatory movement of the vane in a generally cylindrical fluid operating chamber between opposite sides of a radial stator are well known as evidenced by U.S. Pat. Nos. 3,128,679; 3,131,610 and 3,215,046. U.S. Pat. Nos. 4,495,856 and 4,656,925 describe rotary actuators of this general type having improved seals for preventing leakage of fluid from the operating chamber of the actuator to the ambient and for preventing leakage of the operating fluid from the high pressure side to the low pressure side of the chamber around the end surfaces of the vane and the stator.
When rotary actuators using the prior art type seals have been used as torque resistances, such as in exercise machines, the initial or break-away resistance provided by the seals in the actuators have been greater than desired, and it would therefore, be desirable to provide such actuators with seals having an extremely low break-away or initial resistance.
Also it would be desirable to minimize the axial and radial movement of the shafts in rotary actuators and to minimize the deflection of the end plates against which the ends of the stators and vanes are sealed.